Ophthalmology Quiz 1

Q1 – Match the following

  1. Optic nerve lesion               a.Macular sparing homonymous hemianopia
  2. Optic tract lesion                b. Bitemporal hemianopia
  3. Occipital cortex lesion        c. Homonymous hemianopia
  4. Optic chiasma lesion          d. Ipsilateral blindness

Q2 – Match the following

  1. Low vision aids                 a.Myopia
  2. C3R                                b.Squint
  3. Excimer laser                  c. Macular degeneration
  4. Prism                              d. Keratoconus

Answers for Q1

1. Optic nerve lesion – causes ipsilateral blindness. Papillary reflexes, both direct and
consensual will be absent on that side.
2. Optic tract lesion- optic tract lesion causes homonymous hemianopia.
3. Occipital cortex lesion- occipital cortex lesion causes homonymous hemianopia
with macular sparing.
4. Optic chiasma lesion – Bitemporal hemianopia
Macular sparing
Macular sparing is when the central 5-10 degrees of the visual field is unaffected in an otherwise hemianopic defect( a defect that affects one half of the field, if its two half of the temporal affected, it is bitemporal hemianopic and likewise for nasal). It is a common characteristic of visual field defects arising from supra-geniculate lesions.Numberous explanations have been put forward to account for macular sparing. Currently, there are three plausible theories:
(1) Shifts in ocular fixation.
(2) Separate blood supply
(3) Extent of macular representation
Up next, each theories explained.
(1) Shifts in ocular fixation
Patients with hemianopic defects may learn to view objects of interest eccentrically in order to ensure that half of it is not lost within the field defect. In fact, such techniques are regularly taught to partially sighted patients with macular lesions. The theory goes that these patients, when asked to look at the fixation target of the perimeter, continue to view slightly to one side, which results in an apparent macular sparing. Some recent work using a fundus perimeter – an instrument that allows the operator to view the fundus during perimetry and to locate the stimuli at a given retinal site – has demonstrated macular sparing in patients who do not show a shift in fixation( Rohrschneider, 1997). This theory cannot, therefore, explain all cases of macular sparing.
(2) Separate blood supply

The separate blood supplies theory follows from some work done by Smith and Richardson (1996). They demonstrated two interesting points: (i) in some individuals the occipital pole of the visual cortex is supplied by the middle cerebral artery rather than the posterior cereberal artery and (ii) in some patients, there is a horizontal border at the macular between the areas supplied by the posterior temporal artery ( a branch of the posterior cerebral artery) and the area supplied by the middle cerebral artery. Both these findings could explain macular sparing. If an occlusion occurs in either the posterior cerebral artery in a patient whose macular area is supplied by the middle cerebral artery, or in a branch of the posterior cerebral artery which does not supply the macular area, then some macular sparing would result. Some clinical evidence supporting the latter explanation has been provided by Ehlers (1957), who reported on eight cases in which the macular sparing was confined to either the upper or lower quadrant.The separate blood supply theory must not be confused with an earlier theory based upon the belief that there is a dual blood supply to the visual cortex. There is no anatomic evidence of a dual blood supply to the visual cortex( Glaser, 1978)

(3) Extent of macular representation

The final theory to explain macular sparing simply states that the macular area has such a large cortical representation that in any incomplete lesion there is a high probability that some of the macular fibres will be left intact.

Answers For Q2

1. Low vision aids – Macular degeneration

2. C3R – keratoconus

3. Excimer laser – myopia

4. Prism – squint

2 Comments

  1. Dr.Bijoy says:

    Answers published! Check above closed tabs.

  2. Dr. Anshad KP says:

    Q1
    1-d 2-c 3-a 4-b

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